Conventional traffic condition monitoring systems collect data on road conditions from vehicle detectors, traffic monitoring cameras (CCTVs: Closed Circuit Televisions), and the like and transmit the data to an information processing apparatus, which determines traffic jam or calculates the transit time based upon the collected data.
In such a traffic condition monitoring system, however, vehicle detectors, CCTVs, and equipment for transmitting data collected from those devices need to be installed on roads. As a result, conventional traffic condition monitoring systems suffer from an increased cost and an enlarged scale.
Meanwhile, use of the communication infrastructure such as the existing cellular phones has been proposed to monitor traffic conditions.
For example, Patent Literature 1 discloses a “traffic information collection system” configured to wirelessly transmit information including an ID of a mobile station, the type of a vehicle, the current position, the current time, and a vehicle speed from the mobile station to a base station and to transmit that information via a telephone network from the base station to a fixed station, which obtain traffic information, such as the volume of traffic or traffic jam on a road on which the mobile station is present, based upon such information.
In Patent Literature 1, the mobile station has a car navigation device and a cellular phone connected to the car navigation device via a communication adapter, so that information obtained by the car navigation device can wirelessly be transmitted to the base station with the cellular phone while the mobile station is moving. The car navigation device includes a driver control part for playing back a map data stored in such device as a CD-ROM, a GPS receiver for receiving positional information from artificial satellites via an antenna, and a processing unit for displaying the current position of the mobile station on the map and the traveling conditions with a display screen based upon the map data from the driver control part, the positional data from the GPS receiver, the vehicle speed data from a vehicle speed sensor for autonomous navigation, and azimuthal data from an azimuthal sensor. The cellular phone can establish a dial-up connection with the base station and wirelessly transmit data such as a position, a vehicle speed, and a road image received from the processing unit of the car navigation device via the communication adapter to the base station. Furthermore, the cellular phone can transmit the ID assigned to the mobile station, the type of the vehicle, and the current time with a dial number when the cellular phone has a dial-up connection with the base station. In each of the mobile stations, the cellular phone connects to the base station every certain period of time or every certain distance and wirelessly transmits information including data such as the ID, the type of the vehicle, the current time, the position, the vehicle speed, and the road image to the base station. Patent Literature 1 also describes that various types of position measurement devices capable of measuring the position of a mobile station can be used as a position measurement part.
Patent Literature 2 discloses a “data processing apparatus for probe traffic information” that estimates the position of a cellular phone from connection status between a cellular phone and base stations, uses the positional information as probe data, and generates traffic jam information by matching of the probe data with road map data. In this Patent Literature 2, the total traveling distance and time of a cellular phone are measured by detecting principal positions between a base station to which a cellular phone first connected to begin a call and a base station from which a cellular phone disconnected to terminate a call, and transit time at which a cellular phone passed these principal positions. The velocity (speed per hour) of the vehicle is calculated from those traveling distance and traveling time.
Patent Literature 3 discloses a “traffic information processing system” that uses communication records of cellular phones from vehicles traveling on roads to collect and distribute traffic information. In Patent Literature 3, a cellular phone with a GPS function has means for acquiring positional information such as the latitude and longitude of its location by wirelessly communicating with artificial satellites. This cellular phone with a GPS function has traffic information distribution request means for requesting a center apparatus to distribute traffic information and positional information transmission means for transmitting its positional information that has been acquired by the GPS function to the center apparatus. The center apparatus has vehicle information collection means for creating traveling data of a vehicle and creating and updating vehicle information data based upon the position and the communication time of a cellular phone having a GPS function. When a cellular phone with a GPS function is operated to start to use a traffic information distribution service, the traffic information distribution request means of the cellular phone transmits a traffic information distribution request to the center apparatus via a base station. At the same time, the positional information transmission means of the cellular phone determines the position of the cellular phone with use of artificial satellites and transmits the positional information to the center apparatus.
Meanwhile, in a communication system for cellular phones or the like, a frequency shift can be estimated from a transmission frequency of a communication signal received by a base station. For example, Non-Patent Literature 1 has proposed a method of estimating a frequency shift by observing the phase rotation of a pilot symbol inserted in a communication signal.
Furthermore, Patent Literature 4 discloses an “adaptive control apparatus” that adaptively controls the directivity of an array antenna so as to track each of mobile terminals in a continuous manner. This adaptive control apparatus disclosed in Patent Literature 4 has a setting part for setting parameters required to calculate a weighting factor based upon a received signal before or after combining. This setting part includes a Fourier transform part for performing a Fourier transform on a signal before combining that has been received by one or more antenna elements to calculate a frequency spectrum and a velocity calculation part for calculating a Doppler frequency based upon this frequency spectrum and calculating a relative speed of the mobile terminal.
Moreover, Patent Literature 5 discloses a “traveling speed detection apparatus of a mobile station” in which a base station detects a traveling speed of the mobile station by calculating the maximum Doppler frequency of a received signal from a mobile station. This traveling speed detection apparatus disclosed in Patent Literature 5 has envelope calculation means for calculating an envelope of radio waves received from the mobile station, intersection count calculation means for calculating the number of intersections over a certain period of time between the envelope calculated by the envelope calculation means and each of a plurality of predetermined levels of the received power, maximum value detection means for detecting the maximum value from among the intersection counts of respective predetermined levels that have been calculated by the intersection count calculation means, and traveling speed calculating means for calculating a traveling speed of the mobile station with use of the maximum value of the intersection counts that has been detected by the maximum value detection means.